In waveguide antennas for receiving and transmitting electromagnetic radiation having frequencies in for example the GHz range the largest possible portion of the surface of the antennas should consist of open channels that are densely packed, i.e. are located closely at or at the sides of each other. This results in that the walls between the channels become long and narrow. Manufacturing such long channels is impossible using the technology which at present is available for mass production. Waveguide antennas having such channels are for example disclosed in the published International patent application WO 94/11920.
Waveguide channels for microwaves are generally often made as metal tubes having accurate internal dimensions. Due to the required high accuracy the manufacture is costly and such channels therefore have high prices.